The present invention is directed to syringes for hypodermic needles, and in particular to syringes which are configured to enable the use of prepared ampoules, which ampoules contain a measured amount of medicinal or other liquid, and which are inserted into the syringe, and removed and discarded after use. Such ampoules typically are formed as a glass cylinder having a puncturable seal at one end. A rubber stopper closes the other end to retain the liquid in the ampoule. The rubber stopper is configured to act as a plunger piston, capable of being pushed along the length of the cylinder, so long as the liquid is capable of escaping from the other end of the ampoule via a needle piercing the puncturable seal.
A typical prior art syringe, which employs such exchangeable ampoules, comprises a syringe body, which may be a hollow substantially cylindrical shell, which has openings at its forward and rearward ends, as well as at least one lateral opening. A plunger assembly is attachable to the rearward end of the syringe body. The plunger assembly usually includes an outer collar which may be internally threaded, so as to screw onto external threads on the rearward end of the syringe body. A plunger shaft is centered within the collar, and capable of sliding axially relative to the collar. On the forward end of the plunger shaft a hook, which emanates from a disk having a diameter slightly greater than that of the plunger shaft, is provided to engage the plunger piston in the ampoule. At the rearward end of the plunger shaft, a thumb ring or other gripping device is provided to enable both forward and rearward force to be applied by the operator.
An inner collar is also slidingly arranged around the plunger shaft, and constrained to move, only between the disk on the plunger shaft, and the outer collar. The inner collar has a diameter less than the interior diameter of the syringe body, but equal or greater than that of the ampoule, and is arranged with the plunger shaft, so that when the plunger shaft is moved forward, the inner collar can remain stationary, pressed against the ampoule by a slightly compressed spring situated in a central well in the outer collar. The inner collar also has a central well, so that when the plunger shaft is drawn rearward, away from the ampoule, the disk and hook are capable of receding into the central well, below the level of the outer rim of the collar, before the disk actually engages the inner collar, and upon continued rearward force, begins to pull the inner collar in the rearward direction.
At the forward end of the syringe body, a coupling for receiving a needle assembly is provided. A typical needle assembly is a cap member, through which a hollow needle member projects in both direction, with sharp beveled openings at both ends of the needle member. The coupling is usually a cylindrical projection having external threading thereon. The cap member will have corresponding internal threading. An aperture, wide enough for the rearward end of the needle member to pass, is provided in the center of the coupling, and leads to the interior of the syringe body. Present needle assembly constructions are intended to be disposable after one use, to prevent the inadvertent transmission of disease, and eliminate the cost and effort incurred by sterilization procedures.
When the syringe is in an unloaded, unstressed condition, the distance between the inner collar of the plunger assembly and the inner surface of the forward end of the syringe body is less than the length of the typical medicinal ampoule. To enable insertion of the ampoule, the plunger shaft must be drawn rearward against the force of the spring in the central well of the outer collar. After insertion of the ampoule, and release of the plunger shaft, the inner collar, under the bias of the spring, presses the ampoule against the forward inner surface of the syringe body, to help maintain it securely in place. In addition, as the ampoule is pressed forward, the seal comes up against the interior end of the needle member, which pierces the seal and extends into the ampoule, enabling the liquid therein to be driven out, upon pressing of the plunger shaft.
As an additional measure of security, for example, to prevent lateral movement of the ampoule during the process of locating the needle or during the process of pressing the plunger shaft, the lateral opening in the side of the syringe body is wide enough, but not long enough to enable the ampoule to be directly inserted, when the syringe is in the initial unloaded configuration. However, when the plunger shaft is pulled rearwardly enough to move the inner collar, the ampoule may be pivoted and inserted through the aperture. In the typical configuration, the ampoule must be inserted rear end first. When the plunger shaft is released, the inner collar pushes the ampoule forward, until the front end of the ampoule is substantially surrounded by the syringe body and the ampoule cannot be dislodged.
Once the ampoule has been loaded, the operator pushes on the thumb ring, to embed the hook into the plunger piston, bringing the disk flush against the plunger piston. The operator then executes the injection procedure. Once finished, the operator withdraws the needle and prepares to remove the ampoule by drawing back on the thumb ring, to pull the plunger shaft out of the ampoule. Further rearward force on the thumb ring will draw the disk, against the force of the spring, into the central well of the inner collar, ultimately to move the inner collar rearward, away from the ampoule. A problem arises, however, in that once the plunger shaft has been withdrawn from "inside" the ampoule, the ampoule cannot be readily removed from within the syringe body. The seal at the forward end of the ampoule exerts sufficient force on the interior needle end that external rearward force must be applied to back the ampoule off of the interior needle end and enable the ampoule to be removed from the syringe body.
While this may not be a significant problem in the event that only a single ampoule is to be used for a single patient, as the needle assembly might be removed first, it is frequently the case that multiple ampoules/injections will be desired or necessary for a single patient. For the operator to have to employ two-handed effort to replace each ampoule is inefficient, slows the treatment procedure, and increases the potential for injury, contamination, and so on.
Accordingly, it would be desirable to provide a syringe which is adapted to use interchangeable, disposable ampoules, with a means for assuring alignment of the ampoule with the loading/unloading aperture, to enable assured ejection of the used ampoule with only one-handed manipulation required.
The previously described prior art syringe also employs a needle assembly in which the needle is supported and centered by a needle retainer member which is screwed onto a coupling projecting from the front of the syringe body.
It would be desirable to provide a syringe apparatus in which the needle assembly is configured to be removed more easily. For the very same health and sanitation reasons for which the needle assemblies are being made disposable, it is desirable as well to provide a needle assembly which does not require the use of two hands in order to affect its separation from the syringe body. Even more desirable would be a way to eject the spent needle assembly without having to actually touch the needle assembly.
An additional consideration is that the needle tip should be sheathed prior to mounting upon the syringe body, to prevent accidental injury to the operator or patient, and also to maintain the needle in a sterile condition as long as possible, but also after use, again to prevent injury, and to also preclude possible transmission of disease from the contaminated needle assembly. Conventional cap apparatus must applied to the needle assembly by approaching the assembly directly toward the exposed needle point, which presents an undesirable risk of injury.
It is, accordingly, a further object of the invention to provide for an improved needle assembly construction which provides for the facilitated removal of the spent needle assembly.
Yet another object of the invention is to provide a needle assembly construction which does not require the use of two hands to effect the ejection of the spent needle assembly.
A further object of the invention is to provide a construction which permits the ejection of the needle assembly without requiring the operator to actually touch the spent needle.
A still further object of the invention is to provide an improved cap apparatus which enables facilitated covering of the needle assembly prior to and after usage, with reduced risk of injury and transmission of disease.
These and other objects of the invention will become apparent in light of the present specification, claims and drawings.